Fidelity control



INVENTOR.

x535: i=6 umst m M Fm J L ad m? a v L Won JLL. II F l 1 4 Q i k A w wJuly 25, 1939.

" "Patented July 25, less UNITED STATES ra'rsur orrlcs 2.187.; mmcon-moi.

Delaware Arthur v. names, Tnckahoc, N. 1., am. Haseltine corporation.corporation or Application August is. 1936, Serial No. 95,141 it Claims-(01. 3M)

This invention relates to modulated-carrier signal receivers, and moreparticularly to means for controlling the ildelity of signalreproduction of such receivers. i 3 Various expedients have heretoforebeen proposed for controlling the fidelity .oisignalrepropresent knownsystems 01' fidelity control thus inm volve a compromise betweenfidelity and selectivity. The apparatus which has been proposed torpracticing the above-described methods of indirect fidelity control tallhroadlyv'into two classes, namely: apparatussusceptible to manual ascontrol; and apparatus designed automatically to control the selectivityoi the receiver in accordance with prevailing reception conditions.

Manually operable selectivity control means,

while generally satisfactory in operation. are dilgo iicult tor theunskilled operator to use successtully. Those arrangements which areautomatic in operation eliminate this diiflculty, but their constructioninvolves relatively complicated and expensive circuit apparatus.

- 35 It is an object oi. the presentinvention, therefore. to provide anovel method and means for directly controlling the fidelity ofreproduction of a signal modulated-carrier receiver without in anywaymodifying the action or the selective 4 circuits of the receiver.

It is a mrther object of the invention to provide. in asignalmodulated-carrier receiver, a simple and inexpensive electric circuitarrangement for automatically and directly controlling 5 the fidelity oreproduction of the receiver in-- versely in accordance with theintensity oi a desired received carrier. l a

More specifically. it is an object of the present invention. directly tocontrol the iidelity' a; o modulated-carrier receiver by varying. in arelativeiy n'onselective portion of the receiver. the

modulation depth of the selected incoming modulated carrier.

The invention, as hereinafter describedin de- 55 tail, is illustrated inits application to a radio broadcast receiver of the superheterodynetype. Theobjects of the invention. as set forth above, are realised byutilizing the modulation frequency component oi the selected sign lvoltage to control the gain of at least. one of the amplifier stages 5in the radio-frequency channel of the receiver. The amplifier stagesincluded in this portion of the receiver are usually relativelynonselective, the major portion of the seiectivitybeing achieved in theintermediate-frequency channel 0! the receiver by sharply tuning thepermanently tuned intermediate-frequency selector circuits. The

attenuation of the outer sidehalnd frequency coma ponents oi themodulated carrier voltage resulting from the sharp tuning in thischannel oi the receiver causes the ratio oi the amplitude of thesecomponents to the amplitude oi the sideband frequency components in thevicinity of the carrier trequency at the output of the selectorcircuitsto be diii'erent from that existing in the 5 receivedmodulation-fr ency envelope. However. by controlling the fin oi one ormore 0! the high-frequency amplifier stages inversely in accordance withthe amplitudes of the modulation- .irequency envelope of the selectedmodulation carrier, the sideband frequency components in the vicinity 0!carrier frequency may be suh stantially at ted in these stages withoutsubstantially ailecting the amplification oi the o'u'ter sidebandfrequency components. The result is a go flatteningjoi thefrequency-response characteristic o! the receiver and a substantialimprovement in the fidelity of signal reproduction.

The desired change in the eilectiveness oi the fidelity control means isaccomplished .automatig cally and'insuch a manner that the fidelity o!reproduction oi the receiver varies directly in accordance withthe'intensity of a selected carrier. 7 In one modification oi theinvention. the receiver is equipped with the regressive term ofautomatic 0 amplification control which, as is well known, ischaracterized with a rising A. V. C. characteristic such that increasingselected signal-carrier, input is accompanied by increasi signal output.This increase in the signal detector output is utilized to increase theeii'ectiveness oi the fidelity control means with increasingsignals-carrier intensity, and vice versa. In another embodiment of theinvention progressive automatic amplification control is used inaddition to the regressive m amplification control, and with thiscombination the signal detector output is maintained nearly constant forwide fluctuations in the selectedcarrier intensity. Hence, supplementalmeans are required and are provided for varying the efiectiveness of thefidelity control means to obtain the desired variation in the fidelityof reproduction of the receiver with varying signalcarrier intensity.

The novel features which are believed to be characteristic of theinvention are set forth with particularity in the appended claims. Theinvention itseli, however, both as to its organization and method ofoperation, together with further objects and advantages thereof, willbest be understood by reference to the specification taken in connectionwith the accompanying-drawing, in which the single figure illustratesthe invention as applied to a radio broadcast receiver of thesuperheterodyne type.

Referring now to the single figure ot the drawing, there is shown,partly schematic, a complete superheterodyne receiver comprising atunable radio-frequency selector Ill having its input circuit coupled toan antenna-ground circuit II and its output circuit coupled to the inputcircuit of a radio-frequency amplifier or repeater stage including avacuum tube II. The output electrodes of the, tube I2 are, in turn,coupled to the input circuit of a frequency changer l3. Coupled incascade with the frequency changer l3 are an intermediate-frequencyamplifier I4, a second intermediate-frequency amplifier IS, a signaldetector IS, an audio-frequency amplifier l1, and a translating deviceor sound reproducer I8. The signal detector It comprises a dioderectifier is which operates into a load circuit comprising a resistor2|! shunted by a carrier-frequency bypass condenser 2|. Themodulation-frequency components of the voltage developed across theresistor 2|! are impressed on the input circuit of the audio-frequencyamplifier I! through a coupling condenser 22.

In order to maintain the signal input to the detector it within narrowlimits for a wide range of signal intensities, there is providedautomatic amplification control means comprising a diode rectifier 23coupled to the output of the intermediate-frequency amplifier I4 andoperating into a load circuit including serially-connected resistors 24and 25 shunted respectively by highirequency by-pass condensers 26 and21. The junction point between the elements 242'|, inclusive, isgrounded, as indicated. The rectified voltage developed across theresistor 24 is passed through a filter comprising a series resistor 28and a shunt condenser 29, and is applied negatively to an amplificationcontrol electrode of one or more of the tubes included in theintermediate-frequency amplifiers I4 and ii, the frequency changer I3,and the tube l2 through a connection 33. It will be observed that theform of automatic amplification control described above is regressive asto the radio-irequency amplifier including the tube l2, theintermediatefrequency amplifier l4, and the frequency changer l3, and isprogressive as to the intermediate-frequency amplifier l5. This form oiamplification control provides a substantially fiat A. V. C.characteristic such that the signal input to the detector '6 is nearlyconstant irrespective.

of wide fluctuations of the inputsignal-carrier intensity.

Fidelity control is obtained, as hereinafter explained, by means of aphase-shifting network 30 coupled between the load resistor 20 and acontrol electrode of the amplifier tube l2. In the arrangement shown,the control electrode of the tube l2, to which the phase-shiftingnetwork is coupled, is the second grid removed mm the cathode oi thetube, the first grid being the signal input grid. It will be understoodthat the same grid may, in certain applications, be used for bothpurposes. The application of the fidelity control to a separate grid ispreferable, however, since it ensures complete isolation of the fidelitycontrol circuits from the radio-frequency channe] of the receiver.

For the purpose of rendering the fidelity control means automatic inaction so that the receiver is sharply selective when receiving acarrier of small intensity and is relatively broadly tuned whenreceiving a strong carrier, there is included in the coupling pathbetween the phaseshitting network 30 and the resistor 23 a repeatercomprising a vacuum tube 3|. This tube has its input electrodes coupledto the resistor 20 through a condenser 32 and a, control grid-biasvoltage source 33, and its output electrodes cou-' pled to the inputterminals of the phase-shifting network 30 through a condenser 34, anodepotential being supplied to the tube through a resistor 35. The voltageof the source 33 is selected so that the tube 3| is initially biasedconsiderably beyond cutofl. In order to vary the transmissionefliclency, or gain, of the tube 3|, directly in accordance with theintensity of a selected carrier when the carrier intensity exceeds apredetermined value, the unidirectional voltage developed across theresistor 25 is applied positively to the control electrode of the tubethrough a filter resistor 36 to oppose the negative bias due to thesource 33. It will be understood that the unidirectional voltage acrossthe resistor 25 varies in magnitude directly with changes in theselected signal-carrier strength and that when great enough to overcomethe bias beyond cutoff occasioned by the source 33 renders the tube 3|operative to transmit to the phase-shifting network 30 the alternatingmodulation-freqilency voltage across the utilized portion of theresistor 20. If, desired, the magnitude of the alternating voltage inputto the tube 3| may be rendered adjustable to further vary theeiiectiveness of the fidelity control means by terminating theconnection from the control electrode of the tube 3| to the resistor 20at an adjustable contact 31.

Neglecting for the present the action of the fidelity control means, thereceiver described above is of the conventional superheterodyne type,the operation of which is well understood in the art. In brief, thedesired received signalmodulated carrier intercepted by theantennaground circuit II is selected in the selector system l0,amplified in the amplifier tube l2, converted into a signal-modulatedcarrier of fixed intermediate frequency in the frequency changer l3,further selected and amplified in the intermediate-frequency amplifiersI4 and I5, and supplied to the signal detector Ii for rectification. Themodulation-frequency components of the rectified voltage developedacross the resistor 20 it are transferred through the connection 22 tothe audio-frequency amplifier I'I for amplification, after which theyare supplied to the sound reproducer l3 for audio reproduction. Thesignal input to the detector is maintained within narrow limits for awide range of received signal amplitudes through the action of theautomatic amplification control circuit comprising the rectifier 23, thefilter network 23, 29, and the connection 30', in the manner describedabove.

It was pointed out above that, in the operation of a receiver of thetype described, the selectivity thereof is usually attained primarily inthe intermediate-frequency channel by designing theintermediate-frequency selector circuits to be fairly sharply tuned tothe intermediate-frequency carrier. This is necessary in order toprevent undue interference from strong undesired signals on carrierchannels adjacent that of the desired channel. This means that, in theamplification of the carrier and sidebands in the intermediate-frequencychannel, the outer sideband frequencies are discriminated against infavor of the middle range sideband frequencies,

with the result that frequency distortion is pres-' ent in thereproduced output and poor fidelity is obtained.

Such undesired discrimination is substantially obviated in accordancewith the present invention through the action of the fidelity controlmeans to control the amplification or gain of the radio-frequencyamplifier stage including the tube i2 inversely in accordance with themodulation-frequency components of the received modulated carrier. Tothis end, a unidirectional voltage having an instantaneous amplitudeproportional to the instantaneous amplitude of the modulation-frequencyenvelope of the selected carrier is developed across the load resistorof the detector Hi. This component of voltage is amplified in therepeater tube 3!, is shifted in phase through the operation of thephase-shifting network indicated at 30, and is so applied negatively tothe control electrode of the tube I! that it is in exact phaseopposition to the modulation-frequency component of the selectedmodulated carrier being amplified, and from which the signal-frequencycontrol voltage is derived. It is pointed out that the phase-shiftingnetwork compensates only for the small phase shifts occasioned in theselector circuits included in the units of the receiver between the tubel2 and the detector IS, the desired 180 degree phase reversal of themodulation-frequency voltage being obtained in the repeated stageincluding the tube 3|. The amplification in the tube I2 is, of course,decreased by an amount determined by the instantaneous amplitude of thefeed-back control voltage and, since the instantaneous amplitude of thisvoltage isgreatest at the sideband frequencies nearest theintermediate-carrier frequency, due to the sharp selectivity of theintermediate-frequency channel of the receiver, the amplification of thetube i2 is reduced to the greatest extent forvoltage components of thesefrequencies. The result is, therefore, in effect, a demodulation of theselected carrier, or effective varying of the modulation depth of thecarrier inversely in accordance with the separation of the sidebandfrequencies from the carrier frequency, whereby the width of thefrequency transmission band of the receiver is effectively increased.

It will be understood that the demodulation of the carrier, in themanner described above, occurs only when the strength of the incomingselected carrier is above the predetermined value required to render therepeater tube 3| operative. With signal-carrier strengths above thispredetermined value the transmission efficiency of the tube 3| is varieddirectly with the carrier intensity so that with a strong selectedsignal carrier considerable amplification of the demodulating voltage isobtained in the tube 3 I, with the. result that the incoming carrier isdemodulated to a large degree in the tube i2 and the effective frequencytransmission hand through the receiver is relatively wide, and viceversa.

The necessity for employing the tube 3i and its associated amplificationcontrol circuit results from the use of the particular form of automaticamplification control means illustrated and described above. As waspointed out, this form of amplification control, employing bothregressive and progressive control, is characterized by a fiat A. V. C.characteristic which means that, if two signal carriersof differentintensity but modulated to the same degree are received, the resuitingmodulation frequency voltage developed across the load resistor 20 willbe of substantially the same magnitude in each instance. However, allcommercial forms of automatic amplification control are not as effectiveto maintain the input to the signal detector it within such narrowlimits as that described above. For example, in those receivers whichdepend entirely upon regressive action of the automatic control meansfor amplification control, the input to the signal detector increaseswith increasing signal strength with the result that themodulation-frequency voltage increases also. In those receivers whichare constructed and arranged so that the A. V. C. characteristic risesin the above-described manner, it may be unnecessary to employ the tube3i in the coupling path between the resistor Ill and the thephase-shifting network 30, since the increasing magnitude of themodulation-frequency voltage, with increasing signal strength producedby the relatively imperfect amplification control, may be sufficient toprovide the desired automatic effective expansion and contraction of thefrequency transmission band of the receiver as the signal-carrierstrength varies.

In the arrangements described above, the fidelity of reproduction of thereceiver is controlled by varying the amplification or transmissionefficiency of one or more of the modulated-carrier frequency amplifier,or repeater, stages, effectively to demodulate the selected carrierthrough the application, to a control electrode of the controlled tubeor tubes, of a feed-back voltage of proper phase and polarity andproportional in amplitude to the amplitude of the modulationfrequencyenvelope of the selected carrier. The same result may be accomplished byproperly designing the phase-shifting network 30 to discriminate againstthe middle range frequencies of the sidebands without attenuating theouter sideband frequencies, and applying the voltage output from thephase-shifting network to the control electrode of the tube i2positively so that it is in phase with the modulation-frequency envelopeof the selected modulated-carrier input to the tube I2.

with the latter arrangement, the feed-back voltage is effective toproduce a relatively large increase in the gain or transmissionefiiciency of the tube I! for modulation-frequency components of thesignal corresponding to the outer sideband frequencies and only a smallincrease in the gain of the tube for components of the signal voltagehaving center sideband frequencies. The effect is, therefore, abroadening of the frequency transmission band of the receiver and, byvarying the magnitude of the feed-back voltage directly in accordancewith the intensity of a received carrier in the previously describedmanner, the fidelity of the receiver may be varied so that with strongsignals the desired optimum fidelity is obtained and with weak signalsthe receiver is sharply selective.

Although the fidelity control means has been described as applying acontrol voltage to a single amplifier stage of the receiver, it will beunderstood that more than one stage may be subjected to identicalcontrol if the exigencies of a particular receiver so require. It ispointed out that similar results maybe obtained by applying the controlvoltage to the amplifier tubes of one or more of theintermediate-frequency amplifier stages of the receiver.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious changes and modifications may be made therein without departingfrom the invention, and it is contemplated in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What is claimed is:

1. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage including a vacuum tube havinga control electrode, afrequency-selective network coupled to and following said stage, meansfor deriving from a received modulated carrier selected by said networka voltage having an instantaneous amplitude proportional to theinstantaneous amplitude of the modulation-frequency envelope of saidselected modulated carrier, and mean for compensating at least in partfor the frequency-response characteristic of said network comprisingmeans for applying said voltage to said control electrode to vary thetransmission efliciency of said repeater stage inversely in accordancewith the amplitude of said modulation-frequency envelope of saidcarrier, thereby to control the fidelity of reproduction of saidreceiver.

2. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage including a vacuum tube having a control electrode, afrequency-selective network coupled to and following said stage, meansfor deriving from a received modulated carrier selected by said networka voltage having an instantaneous amplitude proportional to theinstantaneous amplitude of the modulation-frequency envelope of saidselected modulated carrier, and means including phaseshifting means forcompensating at least in part for ,the frequency-response characteristicof said network comprising means for applying said voltage to saidcontrol electrode in the correct phase to vary the transmissioneiiiclency of said repeater stage inversely in accordance with theinstantaneous amplitude of the modulation-frequency envelope of saidselected carrier, thereby to control the fidelity oi reproduction ofsaid receiver.

3. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage including a vacuum tube having a control electrode, afrequency-selective network coupled to and following said stage, adetector coupled to said network, means including said detector forderiving from a received modulated carrier selected by said network avoltage having an instantaneous amplitude, variable with theinstantaneous amplitude of the modulation-frequency envelope of saidselected carrier, and means for compensating at least in part for thefrequency-response characteristic of said network comprising means forapplying said voltage to said control electrode to vary the gain of saidamplifier stage inversely in accordance with the instantaneous amplitudeof the modulation-frequency envelope peater stage,

of said selected carrier, thereby to control the fidelity ofreproduction of said receiver.

4. Ina modulated-carrier signal receiver of the superheterodyne type, aradio-frequency rea frequency-selective network coupled to and followingsaid stage, a frequency converter, a detector, and means including saiddetector for compensating at least in part for the frequency-responsecharacteristic of said network comprising means for varying thetransmission efilciency of said repeater stage inversely in accordancewith the instantaneous amplitude of the modulation-frequency envelope ofa modulated carrier selected by said network, thereby to control thefidelity of reproduction of said receiver.

5. In a modulated-carrier signal receiver of the superheterodyne type, aradio-frequency repeater stage including a vacuum tube having a controlelectrode, a frequency-selective network coupled to and following saidstage, a frequency converter, a detector including a load circuit, andmeans comprising means for applying to said control tween said loadcircuit and said control electrode for compensating at least in part forthe frequency-response characteristic oi said network comprising meanfor applying to said control electrode the modulation-frequency voltagedeveloped across said load circuit to vary the transmission efiiciencyof said repeater stage inversely in accordance with the instantaneousamplitude of the modulation-frequency envelope of said carrier, therebyto control the fidelity of reproduction of said receiver.

6. In a wave signal receiver for receiving a selected signal comprisinga carrier and at least one side-band, a modulated-carrier repeaterstage, a frequency-selective network coupled to and following saidstage, said network being most responsive at frequencies in the vicinityof the carrier frequency, and means for compensating at least in partfor the frequency-response characteristicof said network comprisingmeans for varying the transmission efllciency of said repeater stageinversely in accordance with the instantaneous amplitude of the sidebandfrequency envelope of said amplified signal, thereby to render saidreceiver substantially equally responsive to all frequencies included insaid sideband.

7. In a wave signal receiver for receiving a selected signal comprisinga carrier and at least one sideband, a modulated-carrier repeater stagefor repeating said selected signal including a vacuum tube having acontrol electrode, a irequency-selective network coupled to andfollowing said stage, said network being most responsive at frequenciesin the vicinity of the carrier frequency, a signal detector, meansincluding said detector for deriving from said signal a voltage havingan instantaneous amplitude variable with the instantaneous amplitudes ofthe sideband frequency envelope of saidsignal, and means forcompensating at least in part for the frequencyresponse characteristicof said network comprising means for applying said voltage to saidcontrol electrode to vary the transmission efliciency of said repeatermeans inversely in accordance with the instantaneous amplitude of thesideband frequency envelope of said signal, thereby to render saidreceiver substantially equally responsive to all frequencies included insaid sideband.

8. In a wave signal receiver for receiving a selected signal comprisinga carrier and at least one sideband, a modulated-carrier repeater stagefor repeating said selected signal including a vacuum tube having acontrol electrode, a frequency-selective network coupled to andfollowing said stage, said network being most responsive at frequenciesin the vicinity of the carrier frequency, a signal detector, meansincluding said detector for deriving from said signal a voltage havingan instantaneous amplitude variable with the instantaneous amplitude ofthe sideband frequency envelope of said signal, and means includingphase-shifting means for compensating at least in part for thefrequency-response characteristic of said network comprising means forapplying said voltage to said control electrode in the proper phase tovary the transmission efiiciency of said repeater means inversely inaccordance with the instantaneous amplitude of the sideband frequencyenvelope of said signal, thereby to render said receiver substantiallyequally responsive to all frequencies included in said sideband.

9. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage, a frequencyselective network coupled to and following said stage,means for carrying the transmission efilciency of said repeater stageinversely in accordance with the instantaneous amplitude of themodulation-frequency envelope of a modulated carrier selected by saidnetwork, thereby to con trol the fidelity of reproduction of saidreceiver, and means for varying the efiectiveness of said last-namedmeans to vary the fidelity of reproduction of said receiver directly inaccordance with the intensity of said carrier.

10. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage including a vacuum tube having a control electrode, airequency-selective network coupled to and following said stage, meansfor deriving from a received modulated carrier selected by said networka voltage having an instantaneous amplitude proportional to theinstantaneous amplitude of the modulation-frequency envelopeof saidselected modulated carrier, means for varying the magnitude of saidvoltage directly in accordance with the intensity of said carrier, andmeans for applying said voltage to said control electrode to vary thetransmission efficiency of said repeater stage inversely in accordancewith theinstantaneous amplitude of said voltage, thereby to control thefidelity of reproduction of said receiver.

11. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage including a vacuum tube having a control electrode, afrequency-selective network coupled to and following said stage, meansfor deriving from a received modulated carrier selected by said networka voltage having an instantaneous amplitude proportional to theinstantaneous amplitude of the modulation-frequency envelope of saidselected modulated carrier, automatic amplification control means formaintaining the magnitude of said derived voltage nearly constant forwide variations in the input intensity of said carrier, means forvarying the magnitude of said voltage directly in accordance with theintensity of said carrier, and means for compensating at least in partfor the frequency-response characteristic of said network comprisingmeans for applying said voltage to said control electrode to vary thetransmission efflciency of said repeater stage inversely in accordancewith the instantaneous amplitude thereof, thereby to control thefidelity of reproduction of said receiver. I

12. In a modulated-carrier signal receiver, a

modulated-carrier repeater stage including a vacuum tube having acontrol electrode, a frequency-selective network coupled to andfollowing said stage, means comprising a detector including a loadcircuit for developing across at least a portion of said circuit avoltage having an instantaneous amplitude proportional to theinstantaneous amplitudes of the modulation-irequency envelope of amodulated carrier selected by said network, automatic amplificationcontrol means for maintaining the magnitude of said derived voltagenearly constant for wide fluctuations in the intensity of said carrier,means comprising a repeater for compensating at least in part for thefrequency-response characteristic of said network comprising means forapplying said voltage to said control electrode to vary the transmissionefficiency of said first-named repeater stage inversely in accordancewith the instantaneous amplitude of said voltage, thereby to control thefidelity of said receiver, and means comprising at least a portion ofsaid amplification control means for varying the transmission efiiciencyof said second-named repeater directly in accordance with the intensityof said carrier, whereby the fidelity of reproduction of said receiveris varied directly in accordance with the intensity of said carrier.

13. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage including a vacuum tube having a control electrode, afreefluency-selective network coupled to and following said stage, meansfor deriving from a received modulated carrier selected by said networka voltage having an instantaneous amplitude proportional to theinstantaneous amplitude of the modulation-frequency envelope of aselected modulated carrier, automatic amplification control means forincreasing the magnitude of said derived voltage with increasingintensity of said selected carrier, and means for compensating at leastin part for the frequency-response charac teristic of said networkcomprising means for applying said voltage to said control electrode tovary the transmission efliciency of said repeater stage inversely inaccordance with the instantaneous amplitude of said voltage, thereby tovary the fidelity of reproduction of said receiver directly inaccordance with the intensity of said carrier.

14. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage, a frequencyselective network coupled to and following said stage,and means for varying the transmission efliciency of said repeater stagefor the modulated-carrier frequency signal by an amount proportional tothe instantaneous amplitudes of at least a portion of the frequencycomponents included in the modulation-frequency envelope of a. modulatedcarrier selected by said network, thereby to control the fidelity ofreproduction of said receiver.

15. In a modulated-carrier signal receiver, a modulated-carrier repeaterstage including a vacuum tube having a control electrode, afrequency-selective network coupled to and following said stage, meansfor deriving from a modulated carrier selected by said network a voltagehaving an instantaneous amplitude variable with the amplitudes of atleast a portion of the modulation-frequency components of a selectedmodulated carrier, and means for compensating at least in part for thefrequency-response characteristic of said network comprising means for10 plitude of at least a portion of the modulationfrequency components01' a selected modulated carrier, means for compensating at least inpart for the frequency-response characteristic of said networkcomprising means for, applying said voltage to said control electrode,and means for varying the magnitude of said-voltage to vary the fidelityof reproduction of said receiver directly in accordance with theintensity oi said carrier.

ARTHUR V. LOUGHREN. u

CERTIFI CA TE 0F CORRECTION Patent No. 2,167,1495.

July 25, 1939- ARI'HUR V. LOUGHREN.

It is hereby certified that error appears in the oi the above mimberedpatent requiring corrections; follows:

printed specification Page 1, second column, line 25, for the word"modulation" read modulated; page 1.1., first column; line 0, claim 1for "mean" 25, claim 5,

read means; and second column, line strike out meansfor applying to saidcontrol" and insert instead the words and syllable phase-shifting meanscoupled be-;

first colman, line 25, claim 9, for "carrying" read varying; and thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the record of the case in the Patent Office;

Signed and sealed this 12th day of September, A. D. 1959.

(Seal) Henry Van lradale, Acting commissioner of Patents.

10 plitude of at least a portion of the modulationfrequency components01' a selected modulated carrier, means for compensating at least inpart for the frequency-response characteristic of said networkcomprising means for, applying said voltage to said control electrode,and means for varying the magnitude of said-voltage to vary the fidelityof reproduction of said receiver directly in accordance with theintensity oi said carrier.

ARTHUR V. LOUGHREN. u

CERTIFI CA TE 0F CORRECTION Patent No. 2,167,1495.

July 25, 1939- ARI'HUR V. LOUGHREN.

It is hereby certified that error appears in the oi the above mimberedpatent requiring corrections; follows:

printed specification Page 1, second column, line 25, for the word"modulation" read modulated; page 1.1., first column; line 0, claim 1for "mean" 25, claim 5,

read means; and second column, line strike out meansfor applying to saidcontrol" and insert instead the words and syllable phase-shifting meanscoupled be-;

first colman, line 25, claim 9, for "carrying" read varying; and thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the record of the case in the Patent Office;

Signed and sealed this 12th day of September, A. D. 1959.

(Seal) Henry Van lradale, Acting commissioner of Patents.

